The color of a scene in an image appears different depending on what kind of light source (i.e., what kind of illuminant) was incident on the scene when the image was taken. This is because different illuminants such as incandescent light, fluorescent light, and daylight, have different power spectral distributions. White balance (WB) is the process of removing unrealistic color casts so that objects that appear white in a scene also appear white in an image of that scene. In CMOS image sensors, this problem is solved by adjusting the gains of the three primary color channels: red, green and blue. The capability to do white balancing automatically without user interference is known as automatic white balance (AWB).
The most widely used AWB process is based on the “gray-world” assumption, which states that the average of the color in a scene is gray or colorless. Another commonly used assumption is the “white-world” assumption, which states that the brightest point in a scene is white, meaning that the red, green and blue values at the brightest point in a scene are equal to each other.